If this is your first visit, be sure to
check out the FAQ by clicking the
link above. You may have to register
before you can post: click the register link above to proceed. To start viewing messages,
select the forum that you want to visit from the selection below.

OK, so just ran the figures based on Jonathan's design, and by the time you add up all the parts, you'd be looking a finished cost of over £200 per assembly to make them worthwhile making.
That would include the main assembly (Alu shaft, 30t pulley, sealed 7207 bearings), motor pulley, and belt.

However, that's not how I'd personally mount ballnuts , as that's not how they're meant to be mounted.
The precision surface is the external cylinder of the main nut, which should be contained within a hole, but to mount them that way involves scaling things up a bit, however with a bit of a re-design, it could mean they wouldn't need dismantled to swap belts.

Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

That youtube video is interesting, although they must be using an Rxx (cylindrical screw in) type nut, as the 3D file has a locking collar on the rear, which I can only guess is for locking the nut into the shaft.
Also, they must be relying on the pulley/pulley bolts to preload the bearings, which means you'd have to be very precise with measurements, or rely on shims for adjusting the bearings.

I need to go and sketch a couple ideas.

Avoiding the rubbish customer service from AluminiumWarehouse since July '13.